Process of recovering and utilizing the valuable compounds in spent cooking liquors



July 21, 1931. A mgm-ER 1,815,328

. PROCESS OF RECOVERING AND UTILIZING THE VALUABLE COMPOUNDS IN SPENTCOOKING LIQUORS Original Filed Nov. 23, 1927 Patented July 21, 1931UNITED STATES PATENT oFFicE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE,ASSIGNOR TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A kCORPORATION OFMAINE `:PROCESS OF RECOVERING AND UTILIZING THE VALUABLE COMPOUNDS INSPENT i COOKING LIQUORS 'Original application iiled November 23, 1927,Serial No. 235,335. Divided and this application filed January Thisinvention relates to a process of recovering and utilizing valuablecompounds in spent cooking liquors, and more especially liquors of theclass containing sodium-sulphur compounds.

Various liquors of both acid and alkaline character containingVsodiumnsulphur compounds as the fiber-liberating agents have beenproposed and are now being utilized for the production of pulp from rawcellulosic materials, a typical alkaline liquor of this class beingkraft or sulphate liquor, so

called, and a typical acid liquor being sodiy water, and converting thesmelt solution to a fresh cooking liquor. When the inorganic content ofspent liquors containing sodium-sulphur compounds is smelted, a smeltconsisting of a mixture of essentially onlyvtwo sodium compounds isproduced, one bering sodium carbonate, and the other being` Thus, if thesmelta sodium-sulphur salt. ing takes place in a reducing atmosphere, asmelt containing sodium carbonate and sodium sulphide results; but ifthe smelting takes place in an oxidizing atmosphere, a

, smelt containing sodium carbonate and sodium sulphate results.

I have found that it is often advantageous to remove sodium carbonatefrom the rest of the smelt before preparing fresh cooking In accordancewith the present invention, theV removal of sodium carbonate from therest of the smelt is effected either by taking advantage of thedifference in solubility between the sodium carbonate and the rest ofthe smelt, or by converting it into the relatively insolublebicarbonate. Thus,

Serial N0. 332,724.

if the smelthas been produced in a reducing atmosphere and containssodium carbonate and sodium sulphide, separation of sodium carbonate maybe effected by taking advantage of the marked difference in watersolubility between sodium carbonate and sodium sulphide, the sodiumsulphide being quite soluble even under conditions when sodium carbonateis relatively quite insoluble and crystallizes out of solution. If thesmelt has been produced in an oxidizing atmosphere and contains sodiumsulphate rather than sodium sulphide, separation of a substantial amountof the sodium carbonate may be effected by crystallizing it out.

of the solution while permitting most of the sodium sulphate to remainin solution. Or the smelt solution may be carbonated to convert aportion or all of the sodium carbonate into insoluble bicarbonate andthe insoltain instrumentalities which mayl be e1n' ployed when smeltingis effected inA an .oxidizing atmosphere.

Referring to the drawing, 20 represents a storage tank containing theconcentrated spent liquor, which may, for example, be concentrated spentkraft liquor, sulphite liquor, or mixtures thereof. The liquor is fedinto a smelting furnace 30, in which an oxidizing atmosphere ismaintained so as to produce a smelt containing sodium sulphate andsodium carbonate. The smelt is run into a body of water maintained in adissolving tank 31, to form an aqueous smelt solution.

A substantial amount of sodium carbonate may then be crystallized out ofthe smelt solution while permitting most of the sodium sulphate toremain in solution. Thus, a smelt solution comprising 29 parts of sodiumcarbonate and 13 parts of sodium sulphate at a temperature of, say, 300C., may be cooled to, say, 20@ C., to form a crystalline precipitate ofsodium carbonate containing but a relatively very small amount of sodiumsulphate. After the removal of the crystalline material, the motherliquor contains 1G parts of sodium carbonate and 12 parts of sodiumsulphate, indicating a substantial removal of sodium carbonate and arelatively lowv removal of sodium sulphate. Or I may deliver the smeltsolution (or the mother liquor) into a carbonating tower 32, as shown,wherein it is treated with carbon dioxide, thereby precipitating therelatively insoluble sodium bicarbonate. The precipitated sodiumbicarbonate may be removed as by passing the solution and precipitateinto a. rotary filter 33. rl`lie removed sodium carbonate or bicarbonatemay be acidified to produce an acid sulpliite cooking liquor,V While thesodium sulphate-.containing mother liquor may be delivered to a kraftmill to replace the salt-cake ordinarily there employed to compensatefor losses. Or only a portion of the mother liquor may be used for thispurpose in a kraft mill, the rest being mixed With the sodiumbicarbonate and the mixture acidilied with sulphur dioxide to produce anacidV cooking liquor wherein the ratio of sulphite to sulphate` ishigher than Would be the case if the smelt solution Were acidifiedWithout previous separation of bicarbonate. During` acidification of thebicarbonate to produce sodium sulpliite, carbon dioxide is liberated.This carbon dioxide may be recovered and used for the carbonation ofotliersmelt solutions.

Having thus described certain embodiments of this invention, it isevident to those skilled in the art that various changes and niodiiications might be made therein Without departing` from the spiritor scope of invention as defined in the appended claims. Y

I claim: l. A process which vcomprises smelting the inorganic content ofspent cooking liquor containing sodium-sulphur duce a smelt containingsodium carbonate and sodium sulphate, forming an aqueous smelt solution,carbonating the smelt solution to precipitate sodium bicarbonate, andremoving the precipitated bicarbonate.

2. A process which comprises smelting the inorganic content of spentcooking` liquor containing sodium-sulphur compounds in an oxidizingatmosphere to produce a smelt containing sodium carbonate and sodiumsulphate, forming an aqueous smelt solution, carbonating the smeltsolution to precipitate sodium bicarbonate, re-

moving the precipitated bicarbonate, and

acidifying the bicarbonate to produce an acid cooking` liquor.

compounds in an oxidizing atmosphere to pro-A 3. A process whichcomprises smelting the inorganic content of spent cooking liquorcontaining sodium-sulphur compounds in an oxidizing atmosphere toproduce a smelt containing sodium carbonate inorganic compounds fromspent cooking liquor containing sodium-sulphur compounds for use in bothacid and kraft cooking, which comprises smelting the inorganic contentof suoli spent cooking liquor in an oxidizing atmosphere to produce asmelt@ containing sodium carbonate and sodium sulphate, forming anaqueous smelt solution, carbonating the smelt solution to precipitatesodium bicarbonate, removing the precipitated bicarbonatev andconvertingv the Same into acid sulpliite cooking liquor, and smeltingthe inorganic content of the remaining smelt solution along With theinorganic content of spent kraft liquor for the production of freshkraft cooking liquor.

A process of recovering the valuable inorganic compounds from spent.cooking liquor containing sodium-sulphur compounds for use in both acidand kraft cooking, which comprises smelting the inorganic content ofsuch spent cooking liquor in an oxidizing atmosphere to produce a smeltcontaining sodium carbonate rand sodium sulphate, forming an aqueoussmelt solution, carbonating the smelt solution toV vprecipitate sodiumbicarbonate, removing the precipitated bicarbonate, smelting theinorganic content of a portion of the remaining smelt solution alongwith the inorganic content of spent kraft liquor for the production offresh kraft cooking liquor, mixing the rest of the smelt solution Withthe bicarbonate, and converting the mixture into an acid cooking liquor.

6. A process Which comprises smelting the inorganic content of spentcooking liquor containing sodium-sulphur compounds in an oxidizingatmosphere to produce a smelt containing sodium carbonate and sodiumsulphate, and removing sodium carbonate from the smelt.

7. A process Which comprises smelting the inorganic content of spentcooking liquor containing sodium-sulphur pounds in an oxidizingatmosphere to produce a smelt containing sodium carbonate and sodiumsulphate, forming an raqueous smeltsolution, andcrystallizing out asubstantial amount of sodium carbonate from the smelt solution whilepermitting most of the sodium sulphate to remain in solution.

8. A process which comprises smelting the inorganic content of spentcooking liquor containing sodium-sulphur compounds in an oxidizingatmosphere to produce a smelt containin sodium carbonate and sodiumsulphate, orming an aqueous smelt solution, crystallizing out a substantial amount of sodium carbonate from the smelt solution While permittingmost of the sodium sulphate to remain in solution, removing thecrystallized carbonate, and acidifying the carbonate to produce an acidcooking liquor.

In testimony whereof I have aiixed my signature.

GEORGE A. RICHTER.

